Create CMSBlock via REST API fails with “Specified request cannot be processed.”

I am trying to create a CMS Block in Magento Ver.-2.4.8-p3 via REST API

I send Payload via POST as described in the API Reference.

• POST /V1/cmsBlock

I tried many different versions of Payload, for example

{
  "block": {
    "identifier": "test_identifier",
    "title": "Test title",
    "content": "Test content",
    "active": true
  }
}

but nothing worked. Still getting error 400 Bad Request with

{
  "message": "Specified request cannot be processed."
}

Any idea, why this won’t work? Does anyone have working sample payload?